208 ORIGIN OF SEX AND OF THE SOMA 



FIG. 31. Spirogyra. A, one complete cell with parts of two adjacent 

 cells of the filament of a species with one chloroplast in each cell ; 

 cy., cytoplasm lining the wall ; v, vacuole ; n, nucleus suspended 

 by a group of bridles; cA/., spiral chloroplast; p, pyfenoid. B, 

 surface view of cell of large species with several chloroplasts, 

 showing nucleus (n) lying below, connected with surface by 

 bridles (br.) which run to pyrenoids (p). X about 550. C, zygote 

 formed by conjugation of gamete formed in neighbouring cell 

 (marked < = male) of the same filament with gamete formed 

 in cell marked $ = female. D, five filaments which have 

 taken part in conjugation. On the extreme left filament which 

 has acted as female, and all of whose cells contain zygotes. Next 

 is a filament all of whose cells have acted as male, alternate cells, 

 conjugating with those of the filament on the left and on the 

 right. On the extreme right are two filaments in process of con- 

 jugation successive stages from above downwards (left, male ; 

 right, female). At the top of the right-hand filament a cell (v.c.) 

 which has remained vegetative. (Modified from G. S. West. 



